In today's business climate, industry fortunes rise and fall on whether information is exchanged in an efficient manner. Cell phones, pagers, and the Internet have thrived because each allows businesses to exchange critical market information at a moment's notice. In addition, such technologies allow individuals to keep abreast of recent developments with family and friends. In short, many segments of our modern society require instant access to accurate, up-to-the-minute information.
Digital subscriber line (DSL) technology is one technology that provides users with high-speed data. As networking technology has matured, data rates have increased from 20 kilobits per second in 1975, to 100 megabits per second with modern VDSL. In other words, DSL customers in today's “information age” can receive data approximately 5,000 times as fast as network customers of thirty years ago. To bring customers into this modern “information age”, DSL developers have spent billions of dollars to develop the technology as we now know it. To continue to increase data rates at such a remarkable pace, DSL developers will likely be required to spend significant capital resources for many years to come. Thus, DSL technology showcases the premium that our society places on fast and accurate information.
A DSL communication system includes two modems which communicate over an ordinary telephone line (i.e., a twisted pair of copper wires in a conventional residential telephone system). One popular type of DSL technology uses discrete multi-tone, or DMT, to transmit data over a network. In DMT, the communicating modems divide data over a number of sub-carriers that span the frequency range assigned to DSL. For example, in one DSL implementation, 247 separate sub-carriers, each 4 KHz wide will span the DSL frequency range. Thus, as shown in FIG. 1a and FIG. 1b, one could think of DSL technology as the phone company or service provider dividing the frequency spectrum in a phone line 100 into numerous individual 4-KHz bands (or sub-carriers 102), and then transmitting data over each sub-carrier 102. Thus, by using a modem, a customer in the prior mentioned DSL implementation could receive data over 247 sub-carriers over one phone line, and thereby receive high-speed data.
In various types of DSL, the communicating modems monitor each sub-carrier, and if the noise on one sub-carrier becomes too high, then the communicating modems switch to transfer data on another sub-carrier. Thus, typical DSL systems continually switch data from one sub-carrier to another to provide users a high data rate that has relatively few data errors. Although monitoring the sub-carriers and encoding and decoding messages on each sub-carrier makes DMT computationally complex, it gives DMT the ability to provide users with high speed data connections with relatively few errors.
One specific area in which DSL and other communication systems are progressing is by limiting the number of errors as data is transmitted over the line. Impulse noise is one type of noise in communication systems that can occasionally erase an entire modulated signal for a period of time that is equal to one or more transmitted symbols. In DSL communication systems, this erasure can occur regardless of the number of bits allocated to the entire channel or to particular sub-carriers. Further, the specific time of the erasure is usually unpredictable, except the case of the periodic impulse noise, and frequency of erasures can change depending on the time of the day. Therefore, impulse noise parameters and the frequency of erasures are usually unknown at the time of system installation.
If a communication system uses proper noise protection parameters, it can likely correct data errors. However, prior art solutions do not provide for adequate methods or systems to accurately determine impulse noise protection parameters. Although various protocols have been proposed, none of these proposed protocols specify a monitoring process that provides for an unambiguous value of impulse noise monitoring.